Servo controller with digi rf modem

Anyone tried using the 8ch servo controller thru a serial radio modem?
I have the digi 9xtend…
The controller otherwise worx perfect if I connect it directly to the serial port. The modems also work with other devices (i.e - mouse). Does anyone know the specs on the pololu 8ch serial controller? (i.e - half or full duplex, how many wires it’s using?)

Any input is appreciated. When I send data thru the modem to the controller, both the green and red lights a flashing… I’m using the c# program I’ve downloaded from this site.



Any red light flashing state is indicative of bad serial format, which could be caused by things like glitches on the serial line or the line going low for extended periods (causing a framing error). Your other questions about the serial port aren’t that relevant since the servo controller really need only the serial input (tx line from the computer’s perspective). However, it does echo commands in a full duplex, and the output handshaking lines can be used to control the reset line.

It would help if you gave more details about when the error condition comes up. Try sending one byte at a time and see which one causes the problem.

- Jan

Just to be clear, you’re using this servo controller, right?

We use some of the 9Xtend modules in my lab, although I haven’t interfaced one directly with the Pololu servo controllers. The half-duplex setting only applies to the RS-485 protocol. The Pololu serial servo controller uses the normal (full duplex) RS-232 protocol, so you should set the DIP switches as shown in Figure 2‐01 in the 9Xtend datasheet. You should also be using a straight serial cable without the null modem adapter.

Other than that the default settings should work for you.


yes that is the one i got.i’ll try without the null modem adaptor. I’ll have the whole weekend so ill play with it.
the data always gets to the receiver modem (lites are flashing) but the sx controller wont do anything. I’ll keep you guys posted.
thanx for the help.
(sorry for the ugly post i’m replying from my cell phone)

well I tried it again with no luck. for some reason now I’m not getting any lites at all. When I put the battery on the servo controller, the yellow light comes on and stays on until I send data to it. then the green light just flashes while it’s on my machine’s serial port. If I power it, then put it on the modem, the light immediately goes off. I’ve tried putting the default settings back into the modem, then using the standard dip switch settingas described in the manual but again no luck. I kinda suspected the cable as well but the cable checks out fine. I’ve tried with and without the null modem adapter as well. I’m beginning to think that it’s the program I’m using? Does anyone have a program for the pololu controller? I’ve only tried it with the c# code available from this site. I may try a different controller or a usb radio modem instead.
I’m clueless :frowning:

I’m having a really hard time following what you’re doing or saying. In the first part, are you describing normal operation when not using the RF modem? Do you have the reset jumper in place? If so, the RF modem is probably doing something different with the handshaking line and keeping the servo controller reset. What happens after you remove the jumper?

- Jan

I’ll try removing the jumper. I’ll also try moving it with roborealm as well just in case something is up with the c# code…

Thank you everyove for the help, it is now running :smiley:
I had to remove the reset jumper. Now it works like a charm
I appreciate all the input.

Great; I’m happy it’s working well for you!

- Jan